Functional programming

Functional programming is a programming paradigm that treats computation as the evaluation of mathematical functions and avoids changing-state and mutable data. It emphasizes the application of functions, in contrast to the imperative programming paradigm, which emphasizes changes in state.

History

Functional programming has its roots in lambda calculus, a formal system developed in the 1930s to investigate function definition, function application, and recursion. Many functional programming languages can be viewed as elaborations on the lambda calculus. In the 1950s, the first functional programming language, Lisp, was created by John McCarthy at the Massachusetts Institute of Technology (MIT).

Concepts

Functional programming languages are typically designed around the following key concepts:

First-class and higher-order functions

In functional programming, functions are first-class citizens, meaning that they can be passed as arguments to other functions, returned as values from other functions, and assigned to variables. Higher-order functions are functions that take other functions as their arguments or return them as results.

Pure functions

A function is called pure if it always returns the same result given the same arguments (it is deterministic) and does not cause any observable side effects (such as modifying a global object or a variable).

Immutability

Functional programming languages favor immutable data structures. Once created, data structures are never changed in place. If a change is needed, a new data structure is created instead. This can help avoid issues of data changes in a multi-threaded environment and leads to easier reasoning about program behavior.

Recursion

Functional languages primarily rely on recursion to perform looping or iterative behavior, as opposed to the typical loop constructs seen in imperative languages.

Lazy evaluation

Lazy evaluation is an evaluation strategy which delays the evaluation of an expression until its value is actually needed. This can help improve performance and allows the creation of infinite data structures.

Languages

Some well-known functional programming languages include Haskell, Scheme, Clojure, and Erlang. Each of these languages emphasizes different aspects of functional programming.

Applications

Functional programming is particularly useful in scenarios where immutability, concurrency, and determinism are important. It is widely used in academic settings and industries such as finance, where precise algorithms are critical. Additionally, functional programming concepts have influenced the development of many modern programming languages, including JavaScript, Python, and Ruby.

See also

• Declarative programming
• Side effect
• Functional reactive programming

Further reading

• Structure and Interpretation of Computer Programs
• Purely Functional Data Structures